Electrode for luminous tube and method of making the same



R. NAUTH Dec. 29, 1936.

ELECTRODE FOR LUMINOUS TUBE AND METHOD OF MAKING THE SAME Filed Jan 8, 1955 SPA TTE/QED ALKAL/ COAT/N6 CU MET/IL CU 0-CUO F/LM Fla.

STRONG OX/D/Zl/VG FL AME FIG. 2

ISnnentor PA YMOND N/l U TH @7- ii 7W attorney Fla. 3

Patented Dec. 29, 1936 UNITED STATES PATENT OFFICE ELECTRODE FOR LUMINO'US TUBE AND METHOD OF MAKING THE SAME Application January 8, 1935, Serial No. 861

3 Claims.

This invention relates to luminous tubes of the type employed for advertising purposes, and, more particularly, it has reference to a tube in which the contained gas is an inert gas such as helium or the like, and wherein the current-conducting electrodes are formed of metalhaving a surface coating of its own oxides, andwhich may additionally receive a deposit of a salt or oxide of an alkali or alkaline earth.

It is well known that an inert gas contained in a closed tube and at a very loW pressure, say of the order of eight to fifteen millimeters of mercury, may be made luminescent and will glow by passing through the gas an electric discharge of high potential. Such tubes, formerly regarded as laboratory curiosities, and called Geissler tubes, have recently been adapted to commercial purposes, such as advertising signs.

In creating the effect of luminescence, it has been observed that the color of the glow is a function of the contained gas, and that each gas has a particular potential which must be impressed to obtain the desired result. With a gas such as helium, whose characteristic color is yellow or gold, the potential drop is relatively high in comparison with other gases, such as the more familiar neon, whose color characteristic is red.

It is also well known that high operating voltages have an adverse effect on the electrodes used to convey the current to the tube. One effect is cathodic disintegration, whereby the particles of the electrode are discharged, thereby marring the electrode surface and requiring an even higher voltage to maintain luminescence. Another effect is the adsorption or occlusion of the contained gas by the electrode material, which not only increases the resistance of the electrode to flow of electric current, but simultaneously robs the tube of available gas, thus causing a diminution in pressure, which in turn calls forth an increased operating voltage. A consideration of these effects will indicate that they are cumulative, and, once instituted, augment each other and rapidly decrease the life of the tube.

From these considerations, it will be apparent that the provision of a glow tube containing helium, which is operable at economically attainable voltages, and which tube is also durable and of long life, presents a serious problem. The present invention, therefore, proposes a solution of this problem, by making the electrodes of the glow tube of a metal having a good conductivity, and which is protected by means of a surface film of its own oxide or oxides, and which may be further improved by a coating of a material such as a salt or oxide of one of the alkali or alkaline earth metals.

In proposing the use of oxide coatings for electrodes, and in determining by actual use their entire practicability, I apprehend that there may be some dissent on the basis of previously recorded observations. Thus,- Thompson, in his work, The Conduction of Electricity through Gases, Cambridge, the University Press, 1933, suggests, page 324 of Vol. II, that the increase of fall of potential at a cathode of zinc, copper, or iron, which cccurs after the tube has been used for a short time, is due to the disintegration of an oxide film originally occurring on the new cathode. He also points out, page 325, that a deoxidized cathode exhibits a lower fall of potential, and again emphasizes, page 462, that oxidized metals disintegrate slowly.

From these comments, and others of the same nature, it would follow that oxidized cathodes have been proscribed by those whose opinions are entitled to the highest respect, due to the facts that oxidized coatings appear to affect adversely the fall of potential, and also are subject to disintegration.

Despite these pronouncements, however, I have discovered that oxidized metallic electrodes of suitable size are entirely satisfactory for use in luminous tubes intended for advertising purposes, are not-subject to appreciable disintegration, and, in fact, permit operation of long tubes at relatively low voltages.

In order to distinguish further between the above-noted laboratory results and those contemplated by the present invention, I may note that,

- in actual practice, the voltage applied to the sign is in general a function of the inside diameter of the tube, the length of the tube, and the gas contained therein, and the electrodes should have a relatively high surface area compared to the current impressed. Thus, to take a practical example in which helium is used, electrodes made according to the present invention may be formed of copper tubing of about three-eighths inch outside diameter with a wall thickness of about onethirty-second of an inch, and be about one and a half inches in length. Such an electrode, receiving a current of up to about fifteen milliamperes at thirty thousand volts, will produce a luminous glow in tubes of eight millimeters and 11 feet in length, or 12 millimeter tubes of 20 feet in length. It is with tubes and currents of this order that the present invention is concerned.

In one way of producing electrodes for such tubes, according to the preseht invention, I proceed in accordance with the plan illustrated in the accompanying drawing, wherein:

Fig. 1 is a longitudinal section through an electrode;

' Fig. 2 is a diagrammatic view of an apparatus in which the electrodes may be treated;

Fig. 3 is an enlarged fragmentary view of a part of the device sho in Fjig. 2, with an electrode assembled therewithrand,

Fig. 4 is a plan view showing the electrode assembled in a luminous tube.

Referring first to Fig. 1, the electrode is preferably in the form of a hollow tube I!) having a reduced end portion II, the purposes of which will hereinafter be more fully described. As shown in the figure, the electrode is formed of metallic copper having on the surface thereof a layer of cuprous oxide (C1120) and on which is superimposed a layer of cupric oxide (CuO). Covering this double oxide layer is a further coating of an alkali or alkaline earth oxide or salt. While reference has been made to the metal,

- copper, I have found that other metals, particularly nickel, cobalt, and iron, may also be used and oxidized in a similar fashion. However, for' .use in conjunction with helium gas, I find that the doubly oxidized copper gives the best results.

In Fig. 4, the electrode l0, treated as just described, is shown in an assembled relation with a luminous tube. The tube comprises a visible tube portion l2, in which the glow takes place, and which has as its end an enlarged electrode receiving portion l3. The end ll of the electrode I0 is fitted with a wire l5 and is thereafter fiattened and the ends of the wire 15 extend through the end I of the tube portion I3, which end is also fused and flattened to form a gas-tight seal. The opposite end of the tube is of substantially the same construction, and it will be understood by those skilled in the art that a high potential current is introduced through the wires l5 to the electrodes Hi, to discharge through the rarefied gas contained in the visible tube portion I2.

In order to prepare the electrodes, the following procedure may be used. A wheel 2| is rotatably mounted on a journal 22 above a relatively shallow tank 23 containing a solution of the coating salt. The periphery of the wheel is provided with a plurality of radial cups 24, the structure of which is best shown in Fig. 3. As there illustrated, each cup is of a suitable size to receive snugly the reduced end Ii of the electrode l0, and is also provided with one or more radial holes 25 to provide a free communication from the interior of the electrode to the atmosphere.

A strong oxidizing flame produced by the manifold 26, supplied from a pipe line 21, plays against the electrodes ID as they revolve on the wheel into the bath 23. This flame should be sufficien'tly hot to bring the electrodes to a temperature of about 1000 degrees C. If the speed of the wheel is properly adjusted, as may be readily determined by test and trial methods, it will be found that the copper is converted on its surface to an adherent layer of cuprous oxide,

over which is formed a thinner layer of cupric oxide. This is the condition which is desired.

As the electrodes revolve and enter the bath, the hot metal is quenched and a film of the contained alkali salt is formed on the metallic oxide. This film is formed on the interior, as well as the exterior of the tubing, the steam generated within the tube escaping through the bore of the reduced portion II and the vents 25. It will be found that the steam carries with it some of the solution which deposits within the tubing above the normal level of the solution, thereby providing an effective coating for the interior of the tube.

In treating electrodes of iron, some caution must be exercised to avoid the formation of a black oxide scale which will peel off. It is advantageous in this connection to use an iron containing a proportion of chromium, such, for example, as a chrome steel.

I attribute the advantageous results obtained by this invention to the existence of a photoelectric effect in the oxidized film. This effect, as I conceive it, results in a secondary radiation tending to reduce the potential required to create the discharge. It also appears that by using the double oxide film in combination with the alkali coating, a still further reduction of potential is obtained, and the electrodes are durable in character, do not disintegrate, or adsorb the gas in the tube.

While I have endeavored, in connection with the description of the practical results attainable with this invention, to refer to certain matters of theory, it will be understood that the utility of the invention does not depend on such theoretical considerations, the advantages described existing apart therefrom. It will also be understood that the invention should be construed in the light of the following claims.

I claim:

1. A luminous tube comprising a length of tubing containing an inert gas, electrode portions secured to the ends of said tubing, and electrodes in said electrode portions, said electrodes consisting of copper having, an inner surface layer of cuprous oxide and an outer surface layer of cupric oxide thereon.

2. A luminous tube comprising a length of tubing containing an inert gas, electrode portions secured to the ends of said tubing, and electrodes in said electrode portions, said electrodes consisting of copper having an inner surface layer of cuprous oxide and an outer surface layer of cupric oxide thereon, and a coating of an alkali compound on said cupric oxide coating.

3. A luminous tube comprising a length of tubing containing an inert gas, electrode portions secured to the ends of said tubing, and electrodes in said electrode portions, said electrodes consisting of copper having an inner surface layer of cuprous oxide and an outer surface layer of cupric oxide thereon, and a coating of an alkali compound on said cupric oxide coating, the gas in said tube consisting essentially of helium.

RAYMOND NAUTH. 

